Compression ignition (diesel) engines experience various operational difficulties in cold temperatures. Difficult starting in cold weather can be attributed to various causes: Cold weather reduces the available battery current, decreasing the electrical power available to the engine self-starter. Injected fuel condenses on the cold cylinder surfaces leading to improper atomization, which inhibits formation of a combustible mixture inside the cylinder. The engine lubricating oil tends to thicken, leading to increased friction resisting the starter motor, further taxing a battery that may be operating at a reduced output. Hard starting problems can occur with mobile engines such as those in large trucks, buses and even smaller trucks such as the 6.0L and 6.4L POWER STROKE® diesel engines sold by Ford Motor Company. Engines for fixed installations often also encounter similar difficulties starting in cold weather.
Various systems and devices may be utilized to improve starting in cold weather, including battery heaters (to produce higher battery output), engine block heaters (to reduce oil viscosity and reduce fuel condensation), glow-plugs (installed in the cylinder to assist with combustion) and the like.
Proper lubrication can also be a problem in cold weather operation. The cold diesel fuel injected into the cold cylinders can condense and pass along the cylinder walls, diluting the lubricating oil. Engine lubrication in cold weather can also be a problem. The engine lubricating oil becomes more viscous in cold temperatures reducing its effectiveness in lubricating engine components during startup and initial operation. Consequently, some operators elect to use an very thin oil such as an exemplary 0W-20 to allow for easier cold weather starting. However, once the engine is warmed, the viscosity and therefore the oil film thickness in the bearings and elsewhere may drop below that recommended by manufacturers, allowing metal-to-metal contact at bearing surfaces leading to accelerated wear. Thus, another problem operators of diesel engines encounter during cold weather operation is selecting an oil that will adequately lubricate yet will not contribute unnecessarily to starting difficulties.
Since diesel engines operate in all seasons, hot weather operation is also a consideration. To aid hot weather operation, diesel engines are often equipped with engine oil coolers, which reduce oil temperature during hot driving conditions so as to keep the oil at a proper viscosity level. However, engine oil coolers do not aid engine operation in cold environments where it is often desirable to warm the oil rather than cooling it. If engines having an oil cooler could be fitted with a device to aid cold weather starting and operation then the useful temperature range of a diesel engine and its performance might be improved.